The present invention relates to an optical module for use in an optical communication system using light as an information transmitting medium, such as data link, optical LAN, and so on, and a method of producing the same. In the following description, the optical module comprises at least one sub-module having at least one optical connector, which is fitted in a ferrule of an optical plug and to which an optical operation element (light emitting element or light receiving element) is fixed, and at least one receptacle fitted to the optical plug to prevent the plug from falling off.
Conventionally, an optical module having a plurality of optical connectors (a multi-core optical module) has been produced in such a manner that after single-core optical sub-modules each for optically coupling an optical operation element and an optical fiber with each other have been produced, plural ones of the thus produced single-core optical sub-modules are combined.
Those single-core optical sub-modules may be classified into two, one being a transmitting module using a light emitting element such as a light emitting diode as an optical operation element, the other being a receiving module using a light receiving element such as a pin photo-diode as an optical operation element.
FIG. 1 shows an example of the structure of a conventional single-core optical sub-module. As shown in FIG. 1, in the conventional single-core optical sub-module, an optical operation element (light emitting or light receiving element) 2 is fixed by an adhesive or the like to an optical connector 1 to be fitted in a ferrule (not shown) which is fixed to an end portion of an optical fiber (not shown), after adjusting its optical axis. The optical connector 1 to which the optical operation element 2 is fixed, is fixed to a ceramic package 3 by an adhesive agent or the like. To the ceramic package 3, in addition to the optical connector 1, fixed is a substrate 6 supporting an electronic circuit portion constituted by electronic circuit parts such as a bare chip IC 5 and so on. The bare chip IC 5 and the like mounted on the substrate 6 together with wires connecting them to a wiring pattern on the substrate 6 are sealed by a lid 7 made of kovar etc. In addition, in the ceramic package 3, provided are lead pins 8 constituted by inner leads 8a and outer leads 8b respectively erected from the inner and outer sides of the package. After the inner leads 8a and the electronic circuit portion on the substrate 6 are electrically connected with each other and the electronic circuit portion and terminals of the optical operation element 2 are also electrically connected with each respectively by wire bonding or the like, a cover 10 is fixed to the ceramic package 3 to thereby constitute a single-core optical sub-module.
A plurality of single-core optical sub-modules 11 constituted as described above are assembled to a receptacle 12 as shown in FIGS. 2 and 3 to thereby form a conventional multi-core optical module.
However, the single-core optical sub-module is, as described above, constituted by a number of parts and made up by assembling the respective constituent parts one by one. Therefore, the process of assembling has been complicated and the number of steps required therefor has been large. In addition, since expensive material such as ceramic and so on has been used, reduction of cost or mass-production of the single optical sub-modules has been difficult. In such a circumstance, it has been also difficult to reduce the cost of or to perform mass-production of multi-core optical modules which are constituted by combining a plurality of such single-core optical sub-modules.
In addition, a multi-core optical module is attached/detached to/from a multi-core plug having a plurality of ferrules 13 in the receptacle 12 in practical use, and, therefore, a high positioning accuracy is required in attaching the single-core optical sub-modules 11 to the receptacle 12.
That is, if the positioning accuracy is insufficient, smooth attachment/detachment will be impossible, and in the worst case, abrasion or breakage of the ferrules 13 or the optical connectors 1 will be caused. Conventionally, it has been therefore necessary that the assembling portions of the single-core optical module 11 and the receptacle 12, at which the module 11 is coupled to the receptacle 12, are formed with high dimensional accuracy, and when they are assembled with each other, an alignment tool 15 having aligning ferrules 13, the number of which is the same as that of the optical connectors to be provided in a multi-core optical module to be produced, has been used as shown in FIGS. 2 and 3 to thereby perform accurate positioning. Therefore, together with the reason that the multi-core optical module is constructed by combining single-core optical sub-modules which are difficult to be reduced in their price and to be produced through mass production, it has been very difficult to reduce the price of the multi-core optical modules or to produce them through mass production.
In addition, as shown in FIG. 4, when a multi-core optical module which has been formed through accurate positioning in the above-mentioned manner, is mounted on a printed circuit board 16 by screwing, solder reflowing, or the like, there is a case where the relative positional relationship between the single-core optical sub-modules constituting the multi-core optical module or between the receptacle 12 and each of the single-core optical sub-modules becomes wrong. To prevent this, the expensive aligning tool 15 must be left in such a state that it is attached to the multi-core optical module until the mounting of the multi-core optical module is finished. Accordingly, the workability in mounting has been poor.